1. Field of the Invention
This invention relates to a binocular medical stereomicroscope used in the medical field, especially for dental examination and dental treatment and, more particularly, to a medical binocular stereomicroscope for using an illumination unit as an illumination optical system and arranging the illumination unit in close proximity to an observation optical system to allow effective illumination even upon an undulated area.
2. Description of Related Art
Medical stereomicroscopes are widely used during dental examination, treatment or observation. When using a medical stereomicroscope for dental examination or treatment, the observation target is frequently a tooth or a root canal in which both usually have considerable ruggedness. Therefore, adequate brightness and field depth are required for obtaining a clear visual field. Particularly in a case where there is difference in height within a narrow field, a lower portion would be affected from a shadow of a higher portion; therefore, the creation of a shadow should be restrained as much as possible. Further, when a physician performs examination, treatment, or observation, a sufficient amount of space is required between a lower end portion of a medical stereomicroscope and the targeted affected area.
An example of such medical stereomicroscope will be explained with reference to FIG. 4. First, a structure of an inclined illuminator type microscope will be explained with reference to FIG. 4(a). An inclined illuminator type microscope 51 shown in the figure allows illumination and observation of an observation target 55 without having a common lens (primary objective lens) 54 shared by an observation optical system 52 and an illumination optical system 53. An illumination optical component comprising the illumination optical system 53 is attached at a bottom edge portion of a body tube 51a of the inclined illuminator type microscope 51 and is arranged so that an optical axis 52a of the observation optical system 52 and an optical axis 53a of the illumination optical system 53 coincide at a surface of the observation target 55 in a manner shown in the figure when a plane including two optical axes 52a of the observation optical system 52 is viewed from the side.
Regarding the relation between the optical axis 52a and the optical axis 53a with respect to a plane 57 including the two secondary lenses 56 comprising the observation optical system 52 of the inclined illuminator type microscope 51, the optical axis 53a of the illumination optical system 53 will not be inside a circle 58 when the diameter of the circle 58 is defined as the separated distance between the optical axes 52a of the two observation optical systems 52a. Accordingly, the optical axis 52a and the optical axis 53a coinciding at the surface of the observation target 55 would form a large angle.
Further, FIG. 4(b) is an explanatory view showing a structure of a coaxial illuminator type microscope 59. The coaxial illuminator type microscope 59 shown in the figure allows illumination and observation of the observation target 55 having the common lens (primary objective lens) 54 shared by the observation optical system 52 and an illumination optical system 60. The illumination optical system 60 is arranged inside of a body tube 59a of the coaxial illuminator type microscope 59 and arranged in a position for avoiding a variable magnification optical system 61. That is, the illumination optical system 60 has plural lenses including a prism 60b structured inside the body tube 59a, in which the prism 60b refracts an optical axis 60a for avoiding the variable magnification optical system 61, and then the optical axis 60a coincides with the optical axis 52a of the observation optical system 52 at the surface of the observation target 55 via the primary objective lens 54.
Regarding the relation between the optical axis 52a and the optical axis 60a with respect to the plane 57 including the two secondary lenses 56 comprising the observation optical system 52 of the coaxial illuminator type microscope 59, the optical axis 60a of the illumination optical system 60 will not be inside the circle 58 and will be refracted by the primary objective lens 54 in a direction toward the observation target 55 when the diameter of the circle 58 is defined as the separated distance between the optical axes 52a of the two observation optical systems 52a. Accordingly, the optical axis 52a and the optical axis 53a coinciding at the surface of the observation target 55 would form a small angle.
In respect of the foregoing inclined illuminator type microscope, since the optical axis of the observation optical system and the optical axis of the illumination optical system form a large angle, the optical axis of the illumination system will be in a position forming a large angle with respect to the surface of the observation object and result to a problem of the creation of a large shadow upon a subject undulated portion (e.g. root canal) of the observation target when the optical axis of the observation optical system is positioned perpendicular to the surface of the observation target.
Further, since the illumination optical component comprising the illumination optical system is externally attached to the body tube, the illumination optical component including a holder and the like will be exclusively required for the microscope and will be costly.
In respect of the foregoing coaxial illuminator type microscope, since the optical axis of the observation optical system and the optical axis of the illumination optical system form a small angle, illumination could be performed without forming a relatively large shadow upon the subject undulated portion of the observation target. However, since the illumination optical system is structured within the same body tube as the observation optical system, the path of the optical axis of the illumination optical system will be complex, numerous components such as a prism, lenses or the like will be necessary and a problem regarding cost will be raised. Further, the light irradiated from a light guide transmitted through the prism and plural lenses would raise a problem where luminance will attenuate and have a negative influence upon visual field brightness.